The single best way to prevent the flu is to get a flu vaccine each season. There are two types of flu vaccines:

• “Flu shots” — inactivated vaccines (containing killed virus) that are given with a needle. The regular seasonal flu shot is “intramuscular” which means it is injected into muscle (usually in the upper arm). It has been used for decades and is approved for use in people 6 months of age and older, including healthy people, people with chronic medical conditions and pregnant women.

Regular flu shots make up the bulk of the vaccine supply produced for the United States.

A hi-dose vaccine for people 65 and older which also is intramuscular. This vaccine was first made available during the 2010-2011 season.

An intradermal vaccine for people 18 to 64 years of age which is injected with a needle into the “dermis” or skin. This vaccine is being made available for the first time for the 2011-2012 season.

• The nasal–spray flu vaccine — a vaccine made with live, weakened flu viruses that is given as a nasal spray (sometimes called LAIV for “Live Attenuated Influenza Vaccine”). The viruses in the nasal spray vaccine do not cause the flu. LAIV is approved for use in healthy people 2 to 49 years of age who are not pregnant.

About two weeks after vaccination, antibodies develop that protect against influenza virus infection. Flu vaccines will not protect against flu-like illnesses caused by non-influenza viruses.

The seasonal flu vaccine protects against the three influenza viruses that research suggests will be most common.

[ go to CDC site to learn more ]